1. Field of the Invention
The present invention relates generally to electrolytic test apparatus for the examination of the perfection of miniature circuits and, more particularly, relates to electrolytic apparatus for the non-destructive testing of the continuity of such circuits by visual observation of distinctive patterns of varying optical reflectivity of terminals or other electrical parts of such circuits.
2. Description of the Prior Art
Procedures used in the past for testing circuit boards have been of two general kinds. One procedure has involved very careful visual control during each step in the manufacture of the circuit board, followed by point-to-point electrical probe testing, often just after each layer of metal is deposited on the growing structure and at the end of the manufacture according to a program dictated by the nature of the circuit board itself. Such point-to-point testing is aided by conventional apparatus using a visual or auditory alarm and requiring that two electrical probes be used between the various possible combinations of electrical terminals in each circuit supplied for continuity testing and particularly to the various circuit points adjacent metal layers crossing in close proximity over or under circuit nodal points under test for short circuit faults. However, in multiple layer circuits, it generally proves impractical to perform manual point-to-point tests of all possible combinations because only one such multiple layer circuit may be tested at a time. As a consequence, reliance is placed upon testing multiple layer circuits selected as samples, with the attendant high risk of other multiple layer circuits escaping the presumably statistical sampling process and thus going on for incorporation in higher order and very expensive assemblies. While the dual probe test method is sometimes considered to be adequate for use in the development laboratory on a given sample, it is not satisfactory as a reliable method for use in production testing.
A known alternative to the point-to-point manual testing system is a test system designed to operate cooperatively with a digital computer. Here, the computer is programmed to test all of the foregoing possible combinations of short and open circuits. In addition to generation of the required program, a costly interface probing tool must be generated and used to provide the computer with access to all terminals or other points of significance in the entire circuit to be tested. The number of probes that must be located precisely in the probing tool often amounts to 500 to a 1000. This interface tool or multi-probe fixture and the program must generally be changed each time the circuit type to be tested is changed unless the strictest standarization of design is maintained. This type of integrity tester finds a degree of utility in mass manufacture where designs are not altered, but lacks flexibility otherwise. The expense of setting up the device where even moderately spaced apart changes are made in the circuit design is prohibitive.